This invention relates to an initiator which is used to initiate a heat and pressure producing chemical reaction in response to an electrical signal. The produced heat and pressure wave can then be used to initiate further chemical reactions. These chemical reactions produce sufficient heat and pressure to rapidly ignite adjacent materials, such as the gas generating materials used in inflators of vehicle passive restraint airbag systems.
The inflators used in vehicle airbag systems need to deliver sufficient gas to inflate the system's airbag, or cushion, in a very short time frame. They further need to provide safety and reliability both over the extensive temperature range in which modern vehicles are expected to operate, and over the extended lifetime, typically fifteen years, of a modern vehicle.
Inflators for airbag systems generally actuate upon receipt of an electrical signal from a crash sensor located elsewhere on the vehicle body. Such electrical signal is routed to an initiator, often an electrical squib, wherein it creates a hot spot or a spark sufficient to cause ignition of an adjacent relatively small amount of a solid pyrotechnic or explosive material. The ignition of such solid rapidly generates heat and/or a pressure wave which initiates a gas generating chemical reaction in an adjacent relatively large quantity of gas generating material. The reaction products from the igniter may operate to initiate reaction in the gas generant material directly or such products may initially ignite an intermediate igniter material and the mixed reaction products from such intermediate igniter material then be used to ignite the gas generant material.
The initiators normally used in airbag systems have relied on heat and/or pressure to ignite pyrotechnic materials which then ignite an adjacent heat and/or gas generating material. While these systems have performed adequately, special handling of the pyrotechnic material is required during manufacture of the device. Pyrotechnic materials are usually classified as a Class 1 (more specifically, Classes 1.1 and 1.3) material in Department of Transportation (DOT) Shipping Regulations. Special DOT approvals or permits are generally required for the shipment of Class 1 materials.
A number of different types of inflators have been developed for use in airbag systems. One type of inflator simply releases a compressed gas to inflate the cushion. This type requires a relatively large and strong container for storing the compressed gas. As a result, these inflators are relatively large and relatively heavy, both of which are disadvantages to vehicle manufacturers who generally seek to minimize the size and weight of the components used in their vehicles.
A second type of inflator generates gas by the rapid combustion of solid pyrotechnic gas producing materials, such as metal azides. The combustion reaction is typically initiated by a pyrotechnic initiator.
A third type of inflator, referred to as a hybrid inflator, relies on the rapid combustion of solid materials, such as polyvinyl chloride-potassium perchlorate, to produce both gas and heat, which are then mixed with and heat a stored compressed gas. The heat added to the compressed gas raises its temperature causing its pressure and/or volume to increase. The combined gas produced from the combustion reaction and the heated compressed gas is then used to inflate the airbag.
A recently developed inflator is described in U.S. Pat. No. 5,470,104 to Bradley Smith and Karl Rink. This inflator uses the combustion of a fluid fuel with a fluid oxidizer to generate a heated gas which can be used either to directly inflate an airbag, or to heat a further compressed inert gas before using the combined gases to inflate the airbag. The fluid fuel and oxidizer typically is ignited by a pyrotechnic initiator.
Any of the inflators which use solid pyrotechnic gas generating materials, such as metal azides, will produce entrained glowing hot solid particulates in the product gases. In addition, any inflator using a pyrotechnic initiator, even those which use fluid fuels and oxidants as the gas generant, will produce some combustion by-products in the form of solid particulates (smoke). These hot particulates not only can cause serious burns to occupants of the vehicle, they can be a potential source of failure of the fabric or plastic film materials used to form the cushion. Airbag inflators which rely on pyrotechnic gas generating materials usually contain filters to remove the particulates from the product gas before such particulates can contact the cushion. The filters, however, are relatively bulky and heavy, undesireably adding to the system's size and weight.
Moreover, many of the prior art inflators are housed in structures manufactured from materials, such as aluminum, which are significantly weakened at temperatures which could be encountered in a vehicle or warehouse fire. In order to avoid the possibility of the structure becoming weak and disintegrating into pieces which then are propelled throughout the vicinity, these structures normally include a material which causes auto-ignition at a temperature below that at which the structural material is significantly weakened. The pyrotechnic materials normally used in initiators usually have, for a given composition, an intrinsic auto-ignition temperature. Thus, there is no opportunity to adjust, or tailor, the auto-ignition temperature without adjusting the pyrotechnic composition. However, adjusting or changing the pyrotechnic composition can significantly affect other properties of the pyrotechnic, such as burn rate, combustion temperature, shock and vibration sensitivity, electrostatic discharge sensitivity, and gas yield, to name a few. It has, therefore, generally been necessary to rely on a separate additional auto-ignition material to provide auto-ignition at the desired temperature in inflators which rely on pyrotechnic initiators. One recently developed technique of controlling the design and filling of the fuel of a fluid fueled inflator in a containment element is described in recently issued U.S. Pat. No. 5,494,312 to Karl K. Rink. This technique can provide for the containment element to rupture at a preselected temperature which then permits the fuel to mix with adjacently stored oxidant and autoignite.
Recently issued patents to Karl K. Rink et al., U.S. Pat. No. 5,496,062, and to Marcus T. Clark et al., U.S. Pat. No. 5,429,387, describe several versions of an apparatus used in a hybrid inflator, wherein the functions of a low pressure switch, squib and gas generator are combined in a single chamber which is deployed in a further chamber containing the pressurized inert gas of the hybrid inflator. The single chamber contains all, or at least the major portion, of the gas generating material required by the hybrid gas generator or inflator. Opposed diaphragms provided as part of the housing defining the single chamber react to the pressure inside and outside of the chamber to either close or open an electrical circuit, thereby providing an indication of whether or not the sensed pressures are within specification. Upon activation of the gas generator, the gas generating material within the single chamber is ignited by various disclosed devices including a bridgewire resistor, a squib (pyrotechnic) initiator and a hybrid squib. The gas generating material is a liquid fuel in U.S. Pat. No. 5,496,062 and either a solid material or a mixture of gases in U.S. Pat. No. 5,429,387. While this apparatus provides multiple functions, it has many components and is relatively large and complex to assemble. As its overall size is decreased, the assembly of its component parts of diminished size into a device which includes a reliable switch becomes increasingly difficult. Not only is its applicability limited to fluid fueled hybrid inflators, its complex assembly limits its practical application to those hybrid inflators which have relatively large fuel requirements. Accordingly its primary intended use is as an inflator in passenger side airbag systems, which systems typically require the storage of 6 to 8 cubic inches of gas generant. The apparatus may find some use in driver side airbag systems which typically require 2 to 4 cubic inches of gas generant storage volume. They do not presently appear to have reasonable applicability to the relatively small side impact airbag systems. In contrast the present initiator is relatively small, easy to assemble and has broad general applicability.
It is an object of the present invention to provide an initiator which does not rely on solid pyrotechnic materials and which can be used to initiate gas generation in most of the gas generating inflators used in airbag passive restraint systems. The inventive initiators can be used in other systems which require an elevated temperature and/or a pressure or shock wave to initiate a reaction. Their principal use, however, is presently contemplated to be in gas generators, or inflators, for rapidly providing a quantity of non-toxic particle free gas for inflating apparatus, such as the airbag cushions of vehicular passive restraint systems.
A further object of the present invention is to provide an initiator which in addition to its function in initiating reaction in the ignition train, also provides for auto-ignition to occur at preselected temperatures.
Another object is the provision of a gas generator which uses the non-pyrotechnic fueled initiator.
A still further object is the provision of an assembly containing both the inventive initiator and a separate fluid fuel chamber which can be then be assembled into a gas generator as a unit.